Coaxial conductor system



Oct. 22, 1935. .1. F. WENTZ COAXIAL CONDUCTOR SYSTEM Filed Aug. 26, 1932lNl ENmR J. F. WE N 7'2 ATTORNEY of the, tubular conductor UNITED STATESPATENT OFFICE Jesse I. Wants. New

Telephone Labor-atom,

iarly to the design conductor cables.

For the purpose of signaling there have cables comprising one or andmYork, N. Y.,

a corporation of New York York, N. 1., adgnor to Dell Ineorpora 'tod,New

Application August 26, 1932, Serial No. 630,553 4 Claim!- (CL IVs-205)This invention relates to hollow conductors and to the manufacturethereof, and more particuanufacture of coaxial high frequency electricalbeen proposed signaling more coaxial pairs. A

cable of this type is disclosed, for example, in

U. S. Patents October 30, 1934 to H. W.

outer conductors of the coaxial supporting. Not only must 1,978,418 and1,978,419, issued on Dudley. The hollow pairs are selfthey possesssufficient mechanical strength to resist crushing, but also it isnecessary that they be flexible enough to withstand the bending to whichthey are subjected in the processes of manufacture and installation.

In accordance with the is provided a flexible ing a plurality ofprofiled present invention there hollow conductor comprisstrips whichare arranged to engage one another and which are held to a tubular shapeby means ing member.

of an external bind- The electrical and mechanical characteristics whicha tubular conductor must have to make it suitable for use in a coaxialconductor system of the type referred to, are by the use of profiled thespace between the bular conductor much solid material being essary tomaintain tion. The use of for a collapsible composite necessarilyrestricted. The lar conductor not readily obtainable strips. In thefirst place, central conductor and tuis essentially gaseous,

only so interposed as is necthe central conductor in posiintemalsupporting elements structure therefore is thinness of thetubuintroduces another difilculty.

Flexibility, as well as economy, dictates that the wall thickness be ofthe order of thirty thousandths only twenty or of an inch. Diameters maybe as small as a quarter of an inch. With these dimensions it isdifiicult, if not impossible,

to produce a rugged, self -supporting conductor by the use of ordinaryinterlocking profiled strips. A third restriction is imposed on thelength of lay of tlrestrips. Where the and-groove construction, obtainedby spiralling A short lay, although strips are interlocked 7 againstrelative radial movement, as in a tongueadded strength may be the stripswith a short lay. it improves the mechanical characteristics, increasesthe effective resistance and introduces an unthe length of lay be atleast diameter of the conductor. tion of a constmctloll 11} ten timesthe internal The detailed descrippresent invention whereby the foregoingrequirements can be met, will appear hereinafter.

A feature of. the invention is in the method of fabricating the hollowconductor, and more especially in the method of manufacturing and as- 5sembling an insulated coaxial pair. In accordance with this feature theouter conductor of the coaxial pair and the central conductor, togetherwith the insulated structure associated with the latter, are broughttogether during the fabrica- 10 tion of the hollow conductor, wherebythe coaxial assemblage is created by a continuous process.

Another feature of the invention is the machine by which the foregoingmethod is practised.

Other features of the invention will appear in the following detaileddescription of a specific embodiment of the invention. Reference will bemade to the accompanying drawing, in which:

Figs. 1 and 2 represent, respectively, a crosssectional view of a hollowconductor in accordance with the invention, and a profile of one of thestrips;

Fig. 3 shows an assembled conductor:

Fig. 4 is a longitudinal cross-sectional view of a coaxial conductorassemblage;

Figs. 5 and 6 show alternative means for positioning the centralconductor; and

Fig. '1 illustrates a method of fabricating the hollow conductor and acontinuous process of assembling a coaxial pair.

Referring now to Fig. 1, there is shown in crosssection a preferred formof conductor in accordance with the present invention which may be usedto meet the requirements outlined above. The invention, however, it willbe understood, is capable of embodiment in a variety of other andequivalent forms within the scope of the claims appended hereto. Theconductor shown comprises a plurality of arcuate strips I, roughly 2-shaped in profile, arranged in overlapping fashion to form a tube. Forpurposes of analysis the hollow conductor may be considered ascomprising two coaxial tubular layers each made up of a plurality ofstrips arranged with their edges abutting, each strip being integralwith and uniformly overlapping a corresponding strip in the other layer.Binding members 2, 3, wrapped around the assemblage render itself-supporting. It is realized that heretofore hollow conductorscomprising non-interlocking strips have been proposed. In these,however, the thickness of the strips was such that the strips, under theinfluence of external pressure, cooperated as members of an arch tomaintain their relative positions. considering the thinness of theabutting edges of the strips used in the presentstructure it will berealized that the conductor derives its ruggedness only to a slightdegree from such arch action. The strips are so shaped, it will benoted, that a smooth cylindrical surface is presented on the interior ofthe conductor, a feature that is desirable from an electricaltransmission standpoint.

The profile of one of the strips is shown in amplified form in Fig. 2.In a particular instance where the inner diameter of the conductor was0.318 inch, and the thickness 0.020 inch, ten such strips were used toform the conductor. The total width of each strip was approximately0.165 inch. The dimension a across the face of one of the two steppedsegmental portions comprising the strip was 0.100 inch, and thecorresponding dimension b of the other face was the same. The dimensionc, indicating the width of the body of the strip, was 0.035 inch. Bothportions were of equal thickness, in this particular case dimensions dand 6 being both 0.010 inch. It is desirable generally for mechanicalstrength that the ratio of the width of each segmental portion to itsthickness not exceed ten to one. The ratio of conductor circumference tothe width of the segmen tal portion likewise generally need not exceedten to one.

It will be apparent from the proportions of the profile just described,and specifically from the fact that dimensions a and b are equal, thatwhile the edges of the inner portions will be forced into abuttingrelation by the external binding member, the outer portions will beseparated from each other by several thousandths of an inch.

Fig. 3 shows an external view of the assembled conductor. The strips lare bound tightly by a double wrapping of thin tape 2, 8, which ispreferably of metal. Brass and iron, for example, are suitable materialsfor this purpose. The dimensions of the tape are not critical; brasstape 0.125 inch wide and 0.004 inch thick applied with a lay of 0.50inch was found satisfactory in one case.

A coaxial conductor system utilizing the conductor shown in Fig. 3 isrepresented in Fig. 4. The system comprises a hollow outer conductor 4,a central conductor 5, an insulating or separating member 6 andgenerator I. The latter may represent a carrier wave telephone systemadapted to utilize frequencies of the order of a megacycle per second,as disclosed, for example, in H. W. Dudley Patent 1,978,419, supra. Themeans used for separating the two conductors may take a variety offorms. The separating member 8 shown in Fig. 4 consists of a tube ofinsulating material wrapped in a helix about the central conductor.Partially acetylated cotton, washed cotton and crinkled paper have beenfound to be satisfactory materials. Preferably the helical direction ofthe insulation is opposite to that of the conducting tape. In oneparticular case where the inside diameter of the outer conductor was0.275 inch, a inch partially acetylated cotton tape was rolled into atube, twisted and wrapped with a inch lay about the central conductor.

Other separating means are represented in Figs. and 6. The separatorshown in Fig. 5 comprises two threads or strings 8, 9 of suitablematerial twisted together and applied helically to the central conductorIll. The direction of the twist is opposite to that of the spiral, andthe pitch of the latter is slightly less than twice the twisting pitch.The construction is such that the area of contact between separator andthe central conductor is small. An analogous principle of constructionis employed in the embodiment represented in Fig. 6. Separator ll shown5 here comprises a strip or narrow tape of a solid insulating materialsuch as cellulose acetate or other material having great flexibility andtoughness. The strip is first twisted, preferably with a lay ofapproximately five times the diameter 10 of the central conductor I2,and it is then served on the central conductor with an opposite lay ofapproximately twice the twisting pitch. Only distinct points on thenarrow edge of the strip come in contact with the central conductor.

Losses dueto shunt conductance as a result are unusually low. with allof the separators herein disclosed the softness of the material used andthe slight contact made with the outer conductor are such that theseparator does not contribute materially in resisting deformation of theconductor, restoring the conductor to its tubular shape, or preventingthe component profiled strips from twisting.

The method of manufacturing a tubular conductor in accordance with thepresent invention will be explained with reference to Fig. 7. Thisfigure shows not only means for fabricating the outer conductor of acoaxial pair, but also means for simultaneously applying the separatingmember to the central conductor and for assembling the completestructure. Heretofore, in the manufacture of coaxial conductor systems,it was necessary to prepare the outer conductor in relatively shortsections, and to draw through each a corra spondingly short length ofthe central conductorseparator assembly. The assembled sections werethen united and wound on reels. By the present invention the physicallimitations of the prior methods are overcome and it is now possible tomanufacture by a continuous process assembled coaxial conductor pairs ofany desired length.

The segmental strips comprising the hollow conductor may be given therequired profile by drawing, rolling or other suitable process, They arethen wound on a plurality of spools 21 carried on the face of therotatable member 28. From spools 21 the strips pass through a taperingguide 28 and by the cooperation of a corresponding guide member 29 theyare brought into the overlapping relation shown in Fig. 1. Any desiredamount of lay can be introduced by continuously rotating member 20. Theaxial tension required for the operation is provided by capstan 33 aboutwhich the assembled conductor 2! is passed before it is reeled. Thebinding tapes are applied under tension to conductor 2| from spools 8|and 82 carried on rotatable member 30 through the center of which theconductor passes.

. simultaneously with the formation of the tubular conductor the centralconductor 20 with the separating member 22 wound thereon is fedcontinuously through the center of rotating member a 26 and through thecenter of guide member 28, the outer conductor in effect being formedabout the central assemblage. Preferably the separating member 22 isapplied helically to the central conductor 20 as a part of the sameprocess. ll 'or 7 this purpose conductor 20 may be fed under tensionfrom drum 28 through the center of a rotatable member 24 on which iscarried a spool 2| of the separating material. By adjusting the speed ofrotation of member 24 any desired 8900- II ing of the turns of theseparator may be obtained.

Although the present invention has been described with reference tospecific illustrative embodiments of it, it is to be understood thatother and widely different embodiments may occur to those skilled in theart within the scope of the invention as defined by the appended claims.

What is claimed is:

l. A radio frequency transmission system comprising a pair of coaxialconductors connected one as the return for the other, the outer of saidconductors being a hollow tube made up of a plurality of laterallyelongated profiled strips disposed in overlapping relation, each of saidstrips comprising two integral strip-like portions in different tubularlayers laterally offset from each other several times the thickness ofone of said portions, the inner of said portions being arranged withtheir edges abutting to form a smooth, substantially cylindrical innerconducting skin, and an external restricting member adapted to forcesaid abutting portions together to render said conductorself-supporting, the relative angular positions of adjacent strips beingmaintained principally by radial forces exerted on the outer of saidstrip portions.

2. A combination in accordance with the claim next preceding in whichsaid integral strip-like.

portions are offset from each other approximately three times thethickness of said outer conductor.

3. A radio frequency transmission system comprising a pair of coaxialconductors separated by a substantially gaseous dielectric and connectedone as the return for the other, the outer of said conductors being ahollow tube made up of a plu-- rality of overlapping, laterallyelongated strips each comprising a pair of integral strip-like portionslaterally oflset from each other in different planes so that one of saidstrip-like portions enters into the formation of the outer surface ofthe conductor and the other enters into the for- 5 mation of the innersurface, said strips being disposed with the edges of the inner portionsof adjacent strips abutting to provide a smooth, substantiallycylindrical interior surface and with adjacent strips overlapping adistance several times the thickness and about two-thirds the width,respectively, of one of said portions, the internal diameter of saidouter conductor being of the order of fifteen times its thickness androughly three times the width of one of said portions, and an encirclingmember around said conductor holding said abutting edges in contact witheach other.

4. A high frequency transmission system comprising a pair of coaxialconductors connected one as the return for the other, the outer of saidconductors being less than thirty mils in thickness and a fraction of aninch in internal diameter, said outer conductor being made up of aplurality of non-interlocking profiled strips each comprising integral,laterally elongated offset portions in different tubular layers,adjacent strips being disposed with respective portions in differentlayers overlapping a distance of about twothirds the width of one ofsaid portions and with the edges of the inner portions in abuttingrelation so as to form a smooth interior surface, and

a thin tape of ferromagnetic material wound hellcally around said outerconductor maintaining said strips in abutting relation and shieldingsaid pair of conductors from electrical interference.

JESSE F. WEN'I'Z.

